1. Field of the Invention
This invention relates generally to the visualization of an arterial circulation, including e.g. diagnosis of pulmonary embolism and, more particularly, to the visualization of an arterial circulation of using biodegradable microspheres laden with a contrast material, such as an X-ray absorbent or opaque material.
2. Brief Description of the Prior Art
Decreased blood flow to various organs is a danger faced by all mammals, particularly man. A decrease in blood flow to the lungs is especially dangerous, since it is in the lungs that oxygen is incorporated into the blood for distribution throughout the body.
A blood clot in the lungs, which is one cause of decreased blood flow, gives rise to a disease known as pulmonary embolism. This is one of the most difficult diseases to diagnose because the emboli can be small. The emboli are transparent to conventional X-rays and produce only non-specific symptoms.
In the current technology, diagnosis of pulmonary embolism is generally performed by a pulmonary anteriogram, a technique where a catheter is placed through the heart into the pulmonary artery. An X-ray opaque liquid dye (X-ray dye) is injected through the catheter into the lungs, after which an X-ray movie (angiogram)is used to visualize blood flow through the lungs.
There is also a non-invasive method to diagnose pulmonary embolism which utilizes biodegradable albumin aggregates labeled with radioactive technetium 99 m. The technique involves injection of the aggregates into a vein allowing the aggregates to lodge in the lungs. Visualization of the aggregates is performed by a nuclear camera which detects the radioactive emission or so-called "radio-label".
The current technology for diagnosing pulmonary embolism is inadequate due to the fact that patients are hesitant to have this procedure performed routinely. Further, the insertion of a catheter into the heart and lungs is a surgical procedure, limiting use of this method to hospitals and requiring complex equipment to produce acceptable sequential images.
Use of radioactively labeled biodegradable albumin aggregates has several disadvantages. First, the method is very expensive to use because it is radioactively based. Reasons for these high costs include expensive radioactive measuring equipment and the necessity of protecting medical personnel from radiation exposure. Secondly, the radioactively labeled aggregates have a limited shelf-life, ranging from one week to several months. Even where the shelf-life is at the high end of this range, the continuous decay makes frequent recalibration of the testing apparatus necessary. Finally, this type of test is also limited to hospitals because of the expense of obtaining the proper equipment. Aside from the materials, the costs involved in minimizing radiation exposure for these individuals is substantial. Patients are also hesitant to undergo testing involving the insertion of radioactive materials into their bodies. All of these problems result in low usage of this type of test.
In addition to the disadvantages described above, the non-invasive radioactive tests have poor reliability because the resolution of the images is limited and small emboli cannot be detected. The patients must be flat for many minutes to allow sufficient radioactive disintegration to occur in order to provide enough information to create the image. Otherwise, small movement blurs the image thereby limiting image isolation.
Because of the problems and disadvantages associated with current methods of diagnosing pulmonary embolism, there is substantial under-utilization of pulmonary embolism testing in relation to the frequency of occurrence of the disease. What is needed, therefore, is a method of diagnosing pulmonary embolism that is accurate, inexpensive to use, inoffensive to patients and capable of being used in a traditional doctor's office. The present invention satisfies these needs and provides other related advantages.